1. Technical Field
The present invention relates to the energy storage system of an Uninterruptible Power Supply (UPS) equipped with the battery and a method of driving the same and, more particularly, to the energy storage system of a UPS equipped with the battery, wherein some capacity of the battery is used as an energy source by controlling the discharge power of the battery using a rectifier and a bidirectional converter used in the UPS, thereby being capable of reducing the consumption power of a user and using the remaining capacity as reserved power in emergency, and a method of driving the same.
2. Description of the Related Art
Recently, an energy storage system (ESS) that may be said to be the core of a smart grid is a system for storing energy. Various devices for storing energy have been developed. A representative storage device is for storing energy in the battery through a charger during night time for which a power demand is small and for discharging the stored energy through a discharger during time for which a power demand is great. This is commonly called a system association type energy storage system.
In order to store energy, a converter for converging AC into DC and an inverter for converting DC into Ac are basically required. In this case, if a product using DC as an energy source, such as the battery and a super capacitor, is used, an AC/DC conversion converter or a bidirectional converter having a charging/discharging function is also required. An UPS may basically perform AC/DC conversion and DC/AC conversion under the control of a controller and the charging/discharging function using a converter. Furthermore, an additional system for additional system association is required.
The UPS also has a function that is prepared for a case where an uninterruptible device is unable to perform a normal function owing to the failure of elements that form the UPS, such as the power converter and the battery, that is, an energy storage device.
In order to increase the use of an energy storage system based on a physical energy change or chemical energy conversion, lost of efforts have been made in a politic way. More particularly, lots of efforts are being made to development energy storage system technology for the supply of power consecutively, that is, continuously.
The battery has a factor in the reduction of the lifespan according to the number of times of charging and discharging depending on the type of battery. A lead battery is problematic in terms of inspection and management, such as ineffective handling in emergency, because the activation of a chemical substance that forms the battery, the terminal voltage irregularity of the battery, and a change in the generation of corrosion of the terminal unit are not checked. For this reason, a lithium battery further has a function called the battery management system (BMS) in order to prevent the problems and damage attributable to overcharging.
In particular, recently, a reduction of power attributable to the shortage of supply in the peak load of a commercial power source is emphasized. From a viewpoint of power demand management and owing to a difference in a billing system according to each time zone, there is a social and economical need, such as the operation of an emergency generator in order for consumers to manage demands, such as power bill management.
In such a reality, in general, the battery of a UPS owned by a power consumer has a capacity capable of stably supplying power required by the consumer for a specific time that is determined by the consumer, but this is only used when a power failure occurs in a commercial power source. That is, the existing UPS using the battery performs a discharging operation using power of the battery only in the state in which a power failure has occurred in an input power source. Although a momentary power failure occurs, a UPS is inevitably used in a computer server and production equipment that require a lot of time taken for recovery in order to prepare for the momentary power failure.
Examples of technology for solving the problem are disclosed in Patent Documents 1 and 2.
For example, Patent Document 1 discloses a method of estimating the remaining capacity of the battery, including steps of checking whether or not the battery is in the first connection state, checking whether the battery is in a discharging state or a charging state if, as a result of the check, the battery is found to be in the connection state, measuring voltage of the battery if, as a result of the check, the battery is found to be in discharging state, determining whether or not the battery has been stabilized by comparing the voltage of the battery with a predetermined stabilization determination voltage, calculating a voltage drop by calculating the amount of discharged current, calculating an open circuit voltage using the calculated voltage drop voltage and the measured voltage, calculating an initial remaining capacity corresponding to the calculated open circuit voltage, calculating the final remaining capacity using the initial remaining capacity and a predetermined diequilibration efficiency.
Furthermore, Patent Document 2 discloses an apparatus for diagnosing an aging state and a diagnostic method using the same, wherein an ESR value or a loss angle value tan δ are measured by flowing a measurement current signal into the electrolytic capacitor of the DC booth of a power conversion device, the malfunction or damage of the power conversion device is diagnosed based on the measured ESR value or loss angle value, characteristic data, such as internal resistance of each battery to be measured, is measured so that the aging state of the battery system that is an essential element of a UPS can be measured and monitored at the same time, and a complex abnormal state according to the aging or deterioration of the power conversion device is previously monitored diagnosed based on the measured characteristic data.
However, the aforementioned prior arts do not disclose technology in which the battery is used as energy more efficiently in a UPS basically including a rectifier (or a converter), a charging/discharging unit (or a bidirectional converter), an inverter, a bypass, a control board, and the battery.